The present invention relates generally to selective laser sintering and more particularly to temperature control systems for use in part beds of selective laser sintering equipment.
Selective laser sintering is a process that generally consists of producing parts in layers from a laser-fusible powder that is provided one layer at a time. The powder is fused, or sintered, by the application of laser energy that is directed to portions of the powder within a part bed corresponding to the cross-section of the part. After sintering the powder in each layer, a successive layer of powder is applied and the process of sintering portions of the powder corresponding to the cross-section of the part is repeated, with sintered portions of successive layers fusing to sintered portions of previous layers until the part is complete. Accordingly, selective laser sintering is capable of producing parts having relatively complex geometry with relatively acceptable dimensional accuracy and using a variety of materials such as plastics, metals, and ceramics.
Selective laser sintering is well known in the art and has traditionally been employed to produce parts known as xe2x80x9crapid prototypes,xe2x80x9d which are parts that are used to demonstrate a proof of concept or a requirement such as proper form and fit. Generally, the parts are produced directly from an engineering master definition in a CAD (computer aided design) model(s) and thus the time required to produce a rapid prototype is significantly shorter than with conventional methods such as sheet metal forming, machining, molding, or other methods commonly known in the art. Further, the powder materials used to date for selective laser sintering generally have relatively low mechanical properties due to the nature of the rapid prototype application. Accordingly, parts formed using selective laser sintering are typically not used functionally within a design due to limited performance capabilities such as strength or operating temperature.
Existing selective laser sintering equipment controls temperature within the part bed using an infrared sensor, which is physically positioned within the part bed and housed in a cooling jacket to keep a housing of the sensor cool. Unfortunately, the infrared sensor is exposed to gases that are a by-product of the selective laser sintering process, which condense and have a tendency to progressively fog a lens of the infrared sensor throughout a part build. As a result, the infrared signal is reduced and control logic within the selective laser sintering equipment improperly increases the temperature of the part bed, which causes a part cake to become progressively hard or to melt down due to the increased heat. To compensate for such error, an operator typically programs an estimated ramp down of part bed temperature over the depth of the part build. However, part builds often fail and reliability of the selective laser sintering equipment is reduced due to temperature sensing errors.
Accordingly, a need remains in the art for a temperature control system for use in a selective laser sintering machine that accurately and reliably senses temperature within the part bed.
In one preferred form, the present invention provides a temperature control system for use in a selective laser sintering machine that comprises a thermocouple and a temperature transmitter. The thermocouple is preferably disposed on a deck within a part bed of the selective laser sintering machine, and the temperature transmitter is in communication with the thermocouple. Additionally, the temperature transmitter is incorporated into control circuitry of the selective laser sintering machine, and the control circuitry further communicates with control logic of the machine. In operation, the thermocouple senses and communicates part bed temperature to the temperature transmitter, and the control circuitry communicates the part bed temperature to the control logic to control part bed temperature during a part build.
Preferably, the thermocouple is a xe2x80x9cKxe2x80x9d type thermocouple and is disposed adjacent an edge of the deck within the part bed. Output from the thermocouple is transmitted to the temperature transmitter, which is preferably an Omega TX66A/TX67A programmable temperature transmitter. Further, the temperature transmitter is programmed for a known temperature range and for existing control logic within software of the selective laser sintering equipment. In one form of the present invention, the selective laser sintering machine is an SLS 2500 Sintering Machine from the DTM Corporation of Austin, Tex. However, it should be understood by those skilled in the art that other types and models of SLS equipment may be used in accordance with the teachings of the present invention, and the reference to an SLS 2500 Sintering Machine should not be construed as limiting the scope of the present invention.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.